1. Field of the Invention
The present technique relates to an apparatus and a method for correcting defective pixels in imaging signals caused by pixel defects of a solid-state image sensor in an imaging apparatus such as a digital still camera or a digital video camera.
2. Description of the Related Art
In recent years, solid-state image sensors (hereinafter, image sensors), such as CCDs (Charge Coupled Devices) and CMOSs (Complementary Metal-Oxide Semiconductors), are being miniaturized and increased in the number of pixels with the advancement of semiconductor microfabrication technique. On the other hand, with the increase in the number of pixels, some of pixels that do not output a normal signal level in the image sensors, namely, so-called defected pixels also increase in the number.
As a result, the importance of a defective pixel correction technique for electrically interpolating and outputting a signal level to be originally obtained in defective pixels is being increased.
As a defective pixel correction method, for example, a technique described in Japanese Patent Publication No. 3830574 is known. Japanese Patent Publication No. 3830574 discloses a defective pixel correction method to be used in a so-called 3CCD imaging apparatus, which uses three CCDs as image sensors and outputs image signals of three primary colors including red (R), green (G), and blue (B) from the CCDs, respectively.
FIGS. 1A to 1C are explanatory diagrams for describing a defective pixel correction method when a defective pixel is present in an R channel (Rch) color signal.
As shown in FIG. 1A, a case where a defective pixel P(i) is present in an Rch color signal of a captured image is described as an example.
In signals of the same color in which a defective pixel P(i) is present, signal values of normal pixels P(i−1) and P(i+1) before and after the defective pixel Pi are added and averaged as shown in FIG. 1B, so that a linear interpolation value Px is generated. Thereafter, as shown in FIG. 1C, a high-frequency component GH of a pixel on the same position as the defective pixel P(i) is generated based on another color signal different from the color signal where the defective pixel P(i) is present (in FIG. 1C, G channel (Gch)). Thereafter, a correction value GH is added to the linear interpolation value Px, so that a correction process can be performed on the defective pixel P(i) of the Rch color signal.
An imaging apparatus that captures a subject forms a subject image on imaging surfaces of the image sensors via an optical system such as a lens. The image sensors photoelectrically convert light beams incident on the respective pixels so as to output them as electric signals. On the other hand, since the imaging magnification of the lens in the optical system varies with a light wavelength due to magnification chromatic aberration, even when a subject of achromatic color, for example, is imaged, pixel positions on the image sensors where R, G, and B light beams are imaged displace. As a result, an outline or the like of the subject is colored due to color shift.
Unexamined Japanese Patent Publication No. 2006-165899 discloses a defective pixels corrective method in a case where such magnification chromatic aberration of an optical system occurs. Unexamined Japanese Patent Publication No. 2006-165899 discloses a method for selecting a defective pixel correction method according to a position of a defective pixel.